The present invention relates to an image processing apparatus for adding specific information to an input image and outputting the resultant image.
In recent years, the improvements in the performance of color copying machines and color printers have been so great that, they may be successfully used in illegal applications. It is almost impossible to trace an illegally used copying apparatus or its operator from the illegal copies made therefrom.
To prevent illegal copying, the following countermeasure has been attempted. A specific image pattern is registered in a color copying machine or a color printer itself beforehand, and when the pattern on an original is identified by the copying machine or printer, copying is inhibited.
In this case, a circuit for identifying a specific original is used in the color copying machine or color printer. The number of image patterns to be registrable in this circuit is limited. It is, therefore, impossible to register all kinds of originals to be discriminated.
Moreover, in a color copying machine or printer having an external interface, such a circuit for determining a specific original, may not properly function. For example, when image data on the external interface are simultaneously sent as three primary data, i.e., red, green, and blue data, the above determination circuit can be properly operated. However, if image data on the external interface are data such as cyan, magenta, yellow, and black data corresponding to the individual characteristics of a printer, different color-reproducible combinations are present, and a plurality of the types of image patterns for identifying specific originals are required. It is very difficult to even identify and detect a specific original, and the number of images of determinable specific originals is limited. In addition, when image data for expressing the respective color components are surface-sequentially sent in units of colors, image data must be stored in a memory to perform the identification, which results in the use of a high cost memory, thereby requiring a high cost for identifying a specific original.
Assume that the above problem relating to the image data sent from the external interface is solved. Even if the number if specific originals as target objects is limited to the number of recognizable objects, a picture very similar to a registered specific original may be erroneously determined, or a stained specific original may be erroneously determined not to be a specific original. It is impossible to avoid such an error.
It is important to add a means for detecting a specific original in the color copying machine or printer. When an original which is not supposed to be copied is copied, it is important to specify the illegally used copying machine or its operator because the detection capability for identifying specific originals is limited.
Under there circumstances, a technique for adding, to an original image, information which can identify an illegally used copying machine or its operator, has been developed. According to this technique as disclosed in U.S. patent application Ser. No. 07/799,608, of all output color components (e.g., magenta, cyan, yellow, and black) of a copying machine, the output color component (e.g., yellow) which is least noticeable to the human eye is used to modulate (e.g., addition of a predetermined value) the image signal of this output color component. A numeric value or code representing the manufacturing number of the copying machine is formed repeatedly on a reproduced image to every predetermined interval.
In a system proposed along with the developments of performance of color copying machines, and particularly, color readers and configured such that a reader is arranged independently of a printer so that a third party can easily disconnect the reader from the printer, decoding an interface between the reader and the printer with a memory unit and its architecture (e.g., a communication method), fetching an image from the reader, and outputting the decoded data and the fetched image to another printer or computer has been developed to obtain an illegal benefit in practice.
With the above technique, however, although yellow is the output color component which is least noticeable to the human eye, modulation of the corresponding image signal must be minimized. In particular, for example, in a color copying machine used in the fields of design, a problem is posed when a pattern which is not present in an original is noticeable on a reproduced image.
In copying an original, image signals are not necessarily uniform due to variations in sensitivities of a CCD sensor even if a uniform color original is used. When an image in a host computer is printed out using the external interface of a color copying machine, CG (computer graphics) data can be directly output, and a uniform range of image signal levels is necessarily present. At this time, when the yellow component is modulated, an additional pattern undesirably tends to be noticed in a uniform light gray or blue portion or the image.
In a method of defining a numeric value or code representing additional information as a unit pattern and forming an additional pattern by repeating the unit pattern every predetermined interval, the unit pattern is regularly localized and tends to be notice with the human because the human eye can more easily recognize a regular pattern than a random pattern. When the unit pattern is arranged in a matrix form, it tends to be noticed with the human eye. For this reason, the degree of modulation of the image signal must be inevitably reduced, and additional information may not be read depending on the types of specific originals.
Modulation and a pattern which satisfy contradictory conditions, i.e., a condition in which a pattern is unnoticeable in the entire output image and a condition in which the pattern can be properly identified by any method in the copy of a specific original as a target object must be proposed.